My new 6040 improvement plan.

Okay- some interesting results with dial gauge.

In middle of x axis (must be worst deflection zone), I can deflect the machine up or down a staggering 1.3mm! (worried).

I then thought- to prove the theory- deflection must be better or even minimal at either end of X-axis...

Its better, but still 1mm. So looks like its actually entire gantry flexing. Opens new possibilities.

Looking at Y-axis bearings, I previously closed the allen key sdjuster until it stopped, no further. I gave all 4 side screws a wee tweak tighter and deflection has been reduced to 0.4mm at ends and 1.1mm middle of Y axis.

I think theres another adjuster on top of bearing. I'll need to dismantle bed to get to it.

SIGH!

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Originally Posted by magicniner

Go on mate, explain to me just how good they are, and how you'll fix yours :D

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Still incomprehensible to you? :D

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Originally Posted by magicniner

Still incomprehensible to you? :D

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Thanks for that constructive advice, I'll try that!

Now where's that middle finger emoji gone?

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Originally Posted by PaisleyPCdoctor

Thanks for that constructive advice, I'll try that!

Now where's that middle finger emoji gone?

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Here you go -

You can polish it but then it will just be a shiny one ;-)

Regardless of what some people say I think you’re doing a grand job.

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Originally Posted by Kev2960

Regardless of what some people say I think you’re doing a grand job.

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Thanks, mate. Appreciated.

I dismantled machine and nipped up all bolts. I tightened down all bearing adjustment screws (possibly to the point of uneccesary wear- who knows), but after that, the machine felt a whole lot more rigid! I didn't get a chance to measure anything as the wife forced me out into the real world to socialise. I'll measure tomorrow- but deffo better.

Hi there, that’s interesting about the bearing adjuster screws. Can you tell me or send a photo. I might check mine, to be honest I didn’t even know there were any
Kev

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Originally Posted by Kev2960

Hi there, that’s interesting about the bearing adjuster screws. Can you tell me or send a photo. I might check mine, to be honest I didn’t even know there were any
Kev

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Attachment 23423

Aren't those just grub screws holding the bearing cartridge in place? I don't see how those would do any adjusting on the bearings other than distorting the casing or possibly forcing things out of alignment slightly.

My first (well actually second, but first was tiny) CNC machine was a similar design... was good enough to get started with and do light work, but unfortunately you will never be able to address the flex you get on those unsupported rails without just getting rid of them.

Whether that's an issue depends on what the goals are... cutting foam or other very light duty stuff will never show a problem, harder woods or light aluminium work can be done but you have to really work within the limits of the machine and accept that the tolerances and finish may not be what you hope.

They’re probably just plain linear bearings and the screw just stops the bearing rotating or moving in it’s housing.

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Originally Posted by Zeeflyboy

Aren't those just grub screws holding the bearing cartridge in place? I don't see how those would do any adjusting on the bearings other than distorting the casing or possibly forcing things out of alignment slightly.

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Tighten them enough and whatever is under them will eventually apply more pressure on one side of the rod, it isn't an engineering solution but if it works then the only remaining problems are wear and those floppy pesky unsupported rods ;-)

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

When I loosen the grub screws, the gantry flexes as if it's on rubber mounts. Difference is remarkable.

I'm just left with the flexing of the 20mm unsupported x-axis shafts. There's a youtube video where the guy replaces them with supported rails, but improvement was MINIMAL at best. Waste of time.

I have a better, cheaper and easier solution. Just sketching out the plan and I'll post it.

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Originally Posted by PaisleyPCdoctor

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

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Have you tried marking the rod with a marker pen to see if the contact is simply the screw against the rod? ;-)

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Originally Posted by PaisleyPCdoctor

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

When I loosen the grub screws, the gantry flexes as if it's on rubber mounts. Difference is remarkable.

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But that simply isn't how these bearings work, there is no pre-load adjustment... they are just a few rows of bearings inside a tube. You are achieving a reduction in slop most likely by forcing them out of alignment and thus introducing an increased load on one side. It achieves the goal but the problem is that the load isn't evenly distributed and wear will likely be accelerated.

Whatever works for you, but they are retainer screws not adjustment screws.

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I'm just left with the flexing of the 20mm unsupported x-axis shafts. There's a youtube video where the guy replaces them with supported rails, but improvement was MINIMAL at best. Waste of time.

I have a better, cheaper and easier solution. Just sketching out the plan and I'll post it.

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Supported rail doth not equal profile linear rail. My current machine is effectively a 6040 with proper 20mm profile rails and the difference is very obvious compared to the old machine... I don't need a guy on youtube, I've extensively experienced both. Of course even with proper rails you are still left with the general somewhat lightweight design but it's still a significant improvement over the previous model I had with unsupported rails like yours.

I'm not belittling you, you are obviously keen to get stuck in and learn - just be aware that despite what you may think at the moment, those unsupported rails (and to a lesser extent the supported rail on the bottom) are a limiting factor in this machine which you will need to learn to work around and will limit the level of tolerance and finish you can ultimately achieve in harder materials.

An engineer would understand that there is no way to adjust a linear bearing which has at least 4 bearing channels with a single grub screw.

I know you are hoping that you have found the Holy Grail that everyone else has missed but look at the way the system you are messing with actually works and you will understand that you are simply adding side load and wear in an attempt to resolve a problem with tolerance and clearance in the set of components you have unfortunately bought.

- Nick

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Originally Posted by Zeeflyboy

But that simply isn't how these bearings work.

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Don't waste your time!
There are things we understand, there are things we don't understand and there are things which we don't understand why we don't understand them, we are dealing with the third circumstance here :D

If they are simply retaining screws, then fine- they weren't fastened when they built the machine and they are now in their proper location!

It's not like I've torqued them into the rod. Like I said, I screwed them in until they touched/reached resistance then gave them a QUARTER TURN.

The grub screws are obviously put there for a reason and being fully unscrewed (as they were) clearly serves no purpose whatsoever.

The bearings still run smoothly, no crunching or grinding.

The bearings were sloppy, now they are not. Moving on...

I don't think replacing the x axis rails with supported rails will yield much benefit. It looks more work than its worth so I'm going to try a simpler approach.

I'll replace the back panel (3mm aluminium) with 10mm steel plate or possibly 25mm aluminium.

At the top and bottom of my Z axis assembly, I'm going to fit a runner wheel (or 2), adjusted to run tightly along the back plate (rolling along the x axis direction). For the spindle to rock back or forth, it will need to flex the back plate as well as the 2x20mm rails.

I currently cannot see any flexing left and right, just back and forth.

The mod should be cheap, but I will probably need to pay someone to mill some components for me.

I also plan to mill the spindle mounting plate to allow a little tram adjustment left/right tilt. Back/forward tilt should be easy with shims.

But no point until I improve rigidity.

I wouldn't bother tbh... just get it up and running. If you want to revisit ideas later on after having actually put some use on it then do so.

The biggest flex for me on the unsupported rails came from the ability for it to twist (eg apply a force on the bottom of the cutter which is after all where the cutting forces come from) pushing it towards the back of the machine. The top rail will bend forwards and the bottom rail will bend backwards. The deflection is very measurable (and even visible) with quite moderate loads. Your solution of the rear panel doesn't do anything to change that, nor does a single wheel. Two wheels would go someway to solving half the equation (the rail being pushed towards the back) but not the other half (the rail being pulled away from the back). Even then I doubt you would see much benefit with the wheel slop/flex/wear.

In the nicest way possible, don't try to re-invent the wheel on this one. Get your machine up and running, get some use on it and if you find you need to improve on it then feel free, but in all honesty you'll probably come to the conclusion that you are better off building a new machine than trying to improve the 6040.

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Originally Posted by PaisleyPCdoctor

I don't think replacing the x axis rails with supported rails will yield much benefit.

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Cool, let us know how ignoring horribly flexible machine components goes :D

Zee flyboy,
I appreciate your input. Here my thinking.

If you push on spindle, the axis shafts flex. The pivot point is the ball screw, top rod flexes forward, bottom rod flexes back. Vice versa if you pull on spindle.

During this motion, the gantry stays stationary.
The backplate is attached to gantry.

Imagine the gantry didn't need to move left/right on x axis. If I placed a piece of metal from top of z axis to backplate and bottom of z axis to backplate- it would support the spindle and it wouldn't flex. Assuming of course back plate was rigid.

To allow x as is movement- Ill use wheels on the supports.

It'll work.

Yeah but in your example of the Z-axis bolted to the gantry, it can't pull away... a wheel isn't attached to the gantry it just rides on it. Sure it can't push into the gantry (well, beyond what degree flex of the wheel allows) but it can pull away from it. That's not even getting into the problem with swarf getting trapped under the wheels and wearing down the relatively soft aluminium surface.

What you need is something that can't push towards the gantry or pull away from it - ie a supported rail. Round supported rail however has the drawback that the shitty bearing becomes the weak point (even shittier than a fully round rail bearing is)... enter profile rail. Now you come full circle to what I was saying in the first place which is that the unsupported round rail is just inherently inferior to profile rail for milling anything substantial.

Honestly, what you are suggesting is a waste of time - imo the improvements will be minimal if noticeable at all. Combine that rear plate with proper linear rails and now you have a substantial improvement but are at the mercy of the next weak link. And onwards the chase continues.

Listen to me or don't, but I would sincerely suggest you just get cracking with your machine without any major effort/changes and take it from there. I would say after a few mods and chasing your tail you will come to the conclusion that it's better to just chalk it up to a good entry machine for learning/playing around and decide to build your own one rather than constantly trying to work around the inherent weaknesses of the design. Either that or you will decide that for whatever your intended purpose is, it's just fine.

Note that when I say the inherent weaknesses of the design, I'm not just talking about the unsupported rails... there are MANY issues with these machines and to address them all you would effectively end up building a new machine anyway - which is what I am now doing myself.

Just trying to save you some time and money in the process. Up to you if you want to heed that or not.

I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.

I could possibly ADD a really fat supported rail on the other side of backplate, mounted to z axis assembly over and under the backplate.

hmm.

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Originally Posted by Zeeflyboy

Just trying to save you some time and money in the process. Up to you if you want to heed that or not.

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Save your breath, it's a brilliant machine with some little shortcomings which can be resolved with a hex key.

Or Not :-)

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Originally Posted by PaisleyPCdoctor

I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

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I think you underestimate how little it takes to produce chatter

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The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

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Again, the supported rail that you are thinking of is not what I suggest. Supported rail is barely better than round rail... What I am suggesting is profile rail. Everything else you do without doing that is just really little more than pointless.

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BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.

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Good, and I applaud garden shed engineering - it's quintessentially British. Even so, there is limited value in repeating the mistakes of others that have gone before you. One of the great things about our species is the ability to progress based on prior learnings of others rather than being doomed to constantly be stuck in a cycle of repeating the same failures... There is a reason why anything above the absolute most entry level machines use profile rail across hobby/industry and it's not because they weren't creative enough to come up with weird and wonderful solutions like wheels.

Excellent thread !
I very much like the OPs grit-n-go attitude, esp. considering actual measurements re_ flex.

Very Well Done ! keep at it.

The major value to the OP is learning about rigidity, motion control components and actual needs of machine tools in cutting apps.

All others reading this may learn a lot about what is flexible and or sloppy (backlash, jitter, bend aka flex) in these machines, and by about how much, and what happens when you change one part at a time.

The vast majority of people do not ever measure stuff like the OP did re:flex.
The vast majority also give up, usually soon.

I am not giving advice here ... (tend to do too much of that..).

There is a big body of evidence that more or less all machines will do upto about 5x or 500% "better" with some tune-up, mods, and very carefully controlled cutting parameters- for a single specific tuned job when optimised for the machine and tools available.

This applies to the chinese 6040s, bridgeports, small lathes, big lathes.

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Originally Posted by hanermo2

]very carefully controlled cutting parameters

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That part is the most significant by far imo... I've always said the most productive "mod" I ever did for the X2200L was learning to use Fusion360 and figuring out how to best use/tweak adaptive machining for my machine.

Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

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Originally Posted by PaisleyPCdoctor

Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

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You can't do that!
You have previously clearly stated that here's nothing wrong with what you have!
:D

https://www.ebay.co.uk/itm/15-1500mm....c100011.m1850

This is what I used on my gantry I'm very happy with it

You could buy a set of 1500mm with 4 carriages and a set of 300mm with 4 carriages for £200 and then cut the 1500mm down to get the usable lengths of rail to fit X&Y and swap the carriages across.

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Originally Posted by PaisleyPCdoctor

Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

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Seems people have got on fine with Noulei from what I've seen... it'll still be an order of magnitude better than round rail either way. Some good sellers on Aliexpress (I've bought HIWIN there before and been very happy) that will supply to your specs.

Have at least a rough plan though before ordering anything, and do bare in mind that you are addressing one of many mechanical weaknesses in the design... so if the plan is to continue to mod this particular machine, worth having a plan of what comes next and whether that will affect your mods here. For example, to change to profile rail you will likely have to make a new Z-plate and spindle mount. Is it worth changing that over to profile rail as well to avoid having to change it twice? Now your supported rails on the Y-axis are a weak point, then the ridiculous floppy bed, then the thin bendy gantry arms, then the piss poor use of retaining bearings for the ballscrews etc etc.

You see what I mean I hope... Just think it all out (almost like a new machine design) before committing to buying anything.

Then once you've done that and other mods, now you have semi respectable rigidity and realise your extrusions aren't straight enough... at best out come the shims, at worst another redesign. Then you decide you could have done a better job just designing from scratch. It doesn't end :)

They certainly aren't expensive, thanks!

I'll look over the machine and see what the options for mounting are. A big fat back panel will certainly be needed.
Thanks again.

I have original Hiwin's on my Y axis and the clone rail on my X axis they feel identical to me.

That clone rail I linked to is in Germany so no import tax and only took 3 days for delivery for me although will be slower at the moment of course.

At some point it makes more sense just to use it as it for 6 months and then sell it as is and build your own from scratch using the lessons learned along the way.

I bet you'd have no problems selling it for what you paid for it as bad as it might seem it's still better than an xcarve or shapeoko so plenty of potential users out there.

I'm looking at the hiwin hgr15, hgr20 and hgr25. Not a massive price difference for 500mm length.

I'm leaning toward the 20 but only because 15 seems small and 25 is possibly overkill.
I would have 2x rails on x-axis. I have never touched one of these so I'm guessing.

Not gonna jump in and buy straight away, just need to decide so I can mock up with correct dimensions.

Any recommendations would be warmly welcomed. Thanks.

HGR20 is the common choice - HG15 carriages can be very awkward to grease as there isn't a lot of space to get at the grease nipples.

HGR25 is overkill, but on my new machine I ended up using them on the Y-axis just because the dimensions suited my design.

If you're going to fit Hiwin style rails the correct choice is the one that's easiest to retrofit to your existing plates if possible at all.

15mm Hiwin are a PITA to fit with 1605 ballscrew and BK12 fittings you need spacers, I fit my ballscrew sideways on, on my Y axis to solve this problem but still ended up with spacers on the X & Z.

15mm was a no brainer for me, even with the extra hassles but I traded time for my original Hiwin's in the end cost me 12 hours on a Sunday and 6 hours in the week for my 1.2m Hiwin's and 45cm ones on my Z. Was it a good deal? Like my friend tells me my time is worth nothing lol.

So you went with 2x15mm hiwin on your x axis?

I was looking at my machine last night and weighing up the options. I think I can potentially leave my ballscrew and 20mm shafts on and ADD a 15mm hiwin, possibly 2 hiwin. Sounds crazy, but actually looks easier.

My main worry with the 15mm rails- spec says the attaching holes on the trucks are M3 threads. Is that right? Seems a lot of force for 4x M3 screws to handle.